All I found was this. Is it what you are talking about?
WATER AT BONNAROO:
The Bonnaroo Music Festival provides a potable water system for the fans to drink and wash with. Drinking water on this site comes from wells with piping systems to faucets and taps located at guest service areas, Centeroo and the Main Venue. All water provided at taps, faucets and sinks at guest service locations has been tested and certified to meet Drinking Water Requirements in the State of TN. Bonnaroo Staff and the TN Dept of Health test the water daily during the concert to make sure water remains safe to drink.
The onsite water supply may contain sulfur, which is prevalent in the area water supply. Sulfur is a non-metallic element that is prevalent in nature. It exhibits an odor that can be offensive but is not a health risk. Large plastic or metal tanks DO NOT contain water safe to drink. These are for the collection of wastewater.
In an effort to raise awareness of water issues facing the world, reducing waste, and upgrading the drinking water onsite, Bonnaroo and our friends at STANLEY nineteen13 are implementing the Bottle-less Water Program.
It said it on an email, and under the bottle description on the shop page.